The present invention relates broadly to apparatus for manufacturing solid carbon dioxide particles, known to those skilled in the art as carbon dioxide snow. More specifically, the present invention relates to a method and apparatus for facilitating the formation, capture and compression of snow-like carbon dioxide particles into structures that are ready for packaging, use or future processing.
Solid carbon dioxide, or dry ice, has long been used for a variety of desirable cooling purposes. Previous methods of converting liquid carbon dioxide to a solid were slow and required the use of expensive manufacturing equipment.
In one manufacturing method described in Rupp, U.S. Pat. No. 2,570,074, purified carbon dioxide is first passed through a condensing zone to convert the vaporous material to its liquid state. Next, a vent zone receives the liquid carbon dioxide and removes any uncondensed gases. The remaining liquid carbon dioxide is then passed through a reducing valve and flashed into a zone maintained at a uniform temperature and pressure. Crystals that form and settle within this zone are withdrawn from the chamber. A fine spray of water introduced into the zone flows down the sides of the chamber with carbon dioxide solidifying on the surface of the water as carbon dioxide ice. This carbon dioxide ice is then collected and passed to a hopper outside the chamber. Any vaporous carbon dioxide in the chamber may be recycled back into the system after being compressed.
In another dry ice manufacturing process, described in Rupp, U.S. Pat. No. 2,608,838, results were obtained through cooling occurring in the solidification zone by means of a circulating gas. This gas preferably boils at a lower temperature than does carbon dioxide and cooling takes place by directly cooling the carbon dioxide gas. The gas may be a vaporizing refrigerant such as methane, nitrogen, ethane or ethylene.
Love, U.S. Pat. No. 4,415,346 describes a carbon dioxide snow horn for dry ice production that utilizes a downwardly directed skirt opened at its lower, larger diameter end. The upper, smaller diameter head allows introduced liquid carbon dioxide to expand inside the skirt. A gas venting system around the skirt allows exhaust gas to be withdrawn from the chamber.
Manufacturing methods currently in use in the dry ice industry can be complex, inefficient and slow. Production rates of current machines are limited because their operating cycles include separating the solid carbon dioxide particles from a closed volume of carbon dioxide gas (typically by settling) followed by venting of the gas and, finally, compression into solid pellets or blocks. The cycle time is primarily driven by the time it takes for the particles to settle and is typically on the order of 40-50 seconds. As a result, a high capacity machine can typically provide no more than 1500-2500 pounds of dry ice per hour.